PhysicsPhysics (from Ancient Greek: φυσική (ἐπιστήμη),
translit. physikḗ (epistḗmē), lit. 'knowledge of
nature', from φύσις phýsis "nature"[1][2][3]) is the natural
science that studies matter[4] and its motion and behavior through
space and time and that studies the related entities of energy and
force.[5]
PhysicsPhysics is one of the most fundamental scientific
disciplines, and its main goal is to understand how the universe
behaves.[a][6][7][8]
PhysicsPhysics is one of the oldest academic disciplines and, through its
inclusion of astronomy, perhaps the oldest.[9] Over the last two
millennia, physics, chemistry, biology, and certain branches of
mathematics were a part of natural philosophy, but during the
scientific revolution in the 17th century, these natural sciences
emerged as unique research endeavors in their own right.[b] Physics
intersects with many interdisciplinary areas of research, such as
biophysics and quantum chemistry, and the boundaries of physics are
not rigidly defined. New ideas in physics often explain the
fundamental mechanisms studied by other sciences[6] and suggest new
avenues of research in academic disciplines such as mathematics and
philosophy.
Breakthroughs in physics often enable advances in new technologies.
For example, advances in the understanding of electromagnetism and
nuclear physics led directly to the development of new products that
have dramatically transformed modern-day society, such as television,
computers, domestic appliances, and nuclear weapons;[6] advances in
thermodynamics led to the development of industrialization; and
advances in mechanics inspired the development of calculus.

AstronomyAstronomy is the oldest of the natural sciences. The earliest
civilizations dating back to beyond 3000 BCE, such as the
Sumerians, ancient Egyptians, and the Indus Valley Civilization, all
had a predictive knowledge and a basic understanding of the motions of
the Sun, Moon, and stars. The stars and planets were often a target of
worship, believed to represent their gods. While the explanations for
these phenomena were often unscientific and lacking in evidence, these
early observations laid the foundation for later astronomy.[9]
According to Asger Aaboe, the origins of Western astronomy can be
found in Mesopotamia, and all Western efforts in the exact sciences
are descended from late Babylonian astronomy.[11] Egyptian astronomers
left monuments showing knowledge of the constellations and the motions
of the celestial bodies,[12] while Greek poet
HomerHomer wrote of various
celestial objects in his
IliadIliad and Odyssey; later Greek astronomers
provided names, which are still used today, for most constellations
visible from the northern hemisphere.[13]
Natural philosophy
Main article: Natural philosophy
Natural philosophyNatural philosophy has its origins in
GreeceGreece during the Archaic
period, (650 BCE – 480 BCE), when pre-Socratic philosophers like
ThalesThales rejected non-naturalistic explanations for natural phenomena
and proclaimed that every event had a natural cause.[14] They proposed
ideas verified by reason and observation, and many of their hypotheses
proved successful in experiment;[15] for example, atomism was found to
be correct approximately 2000 years after it was first proposed by
LeucippusLeucippus and his pupil Democritus.[16]
PhysicsPhysics in the medieval Islamic world
Main article:
PhysicsPhysics in the medieval Islamic world

The basic way a pinhole camera works

Islamic scholarship had inherited
Aristotelian physicsAristotelian physics from the Greeks
and during the
Islamic Golden AgeIslamic Golden Age developed it further, especially
placing emphasis on observation and a priori reasoning, developing
early forms of the scientific method.
The most notable innovations were in the field of optics and vision,
which came from the works of many scientists like Ibn Sahl, Al-Kindi,
Ibn al-Haytham, Al-Farisi and Avicenna. The most notable work was The
Book of OpticsBook of Optics (also known as Kitāb al-Manāẓir), written by Ibn
al-Haytham, in which he was not only the first to disprove the ancient
Greek idea about vision, but also came up with a new theory. In the
book, he was also the first to study the phenomenon of the camera
obscura (his thousand-year-old version of the pinhole camera) and
delved further into the way the eye itself works. Using dissections
and the knowledge of previous scholars, he was able to begin to
explain how light enters the eye. He asserted that the light ray is
focused, but the actual explanation of how light projected to the back
of the eye had to wait until 1604. His Treatise on
LightLight explained the
world's first camera obscura, hundreds of years before the modern
development of photography.[17]

The seven-volume
Book of OpticsBook of Optics (Kitab al-Manathir) hugely influenced
thinking across disciplines from the theory of visual perception to
the nature of perspective in medieval art, in both the East and the
West, for more than 600 years. Many later European scholars and fellow
polymaths, from
Robert GrossetesteRobert Grosseteste and
Leonardo da VinciLeonardo da Vinci to René
Descartes,
Johannes KeplerJohannes Kepler and Isaac Newton, were in his debt. Indeed,
the influence of Ibn al-Haytham's
OpticsOptics ranks alongside that of
Newton's work of the same title, published 700 years later.
The translation of The
Book of OpticsBook of Optics had a huge impact on Europe.
From it, later European scholars were able to build devices that
replicated those
Ibn al-HaythamIbn al-Haytham had built, and understand the way
light works. From this, such important things as eyeglasses,
magnifying glasses, telescopes, and cameras were developed.
Classical physics
Main article: Classical physics

PhysicsPhysics became a separate science when early modern Europeans used
experimental and quantitative methods to discover what are now
considered to be the laws of physics.[19][page needed]
Major developments in this period include the replacement of the
geocentric model of the solar system with the heliocentric Copernican
model, the laws governing the motion of planetary bodies determined by
Johannes KeplerJohannes Kepler between 1609 and 1619, pioneering work on telescopes
and observational astronomy by
Galileo GalileiGalileo Galilei in the 16th and 17th
Centuries, and Isaac Newton's discovery and unification of the laws of
motion and universal gravitation that would come to bear his name.[20]
Newton also developed calculus,[c] the mathematical study of change,
which provided new mathematical methods for solving physical
problems.[21]
The discovery of new laws in thermodynamics, chemistry, and
electromagnetics resulted from greater research efforts during the
Industrial RevolutionIndustrial Revolution as energy needs increased.[22] The laws
comprising classical physics remain very widely used for objects on
everyday scales travelling at non-relativistic speeds, since they
provide a very close approximation in such situations, and theories
such as quantum mechanics and the theory of relativity simplify to
their classical equivalents at such scales. However, inaccuracies in
classical mechanics for very small objects and very high velocities
led to the development of modern physics in the 20th century.
Modern physics
Main article: Modern physics
See also:
History of special relativityHistory of special relativity and History of quantum
mechanics

Albert EinsteinAlbert Einstein (1879–1955), whose work on the photoelectric effect
and the theory of relativity led to a revolution in 20th century
physics

Modern physicsModern physics began in the early 20th century with the work of Max
Planck in quantum theory and Albert Einstein's theory of relativity.
Both of these theories came about due to inaccuracies in classical
mechanics in certain situations.
Classical mechanicsClassical mechanics predicted a
varying speed of light, which could not be resolved with the constant
speed predicted by
Maxwell's equationsMaxwell's equations of electromagnetism; this
discrepancy was corrected by Einstein's theory of special relativity,
which replaced classical mechanics for fast-moving bodies and allowed
for a constant speed of light.[23]
Black body radiationBlack body radiation provided
another problem for classical physics, which was corrected when Planck
proposed that the excitation of material oscillators is possible only
in discrete steps proportional to their frequency; this, along with
the photoelectric effect and a complete theory predicting discrete
energy levels of electron orbitals, led to the theory of quantum
mechanics taking over from classical physics at very small scales.[24]
Quantum mechanicsQuantum mechanics would come to be pioneered by Werner Heisenberg,
Erwin SchrödingerErwin Schrödinger and Paul Dirac.[24] From this early work, and work
in related fields, the
Standard Model of particle physicsStandard Model of particle physics was
derived.[25] Following the discovery of a particle with properties
consistent with the
Higgs bosonHiggs boson at
CERNCERN in 2012,[26] all fundamental
particles predicted by the standard model, and no others, appear to
exist; however, physics beyond the Standard Model, with theories such
as supersymmetry, is an active area of research.[27] Areas of
mathematics in general are important to this field, such as the study
of probabilities and groups.
Philosophy
Main article:
PhilosophyPhilosophy of physics
In many ways, physics stems from ancient Greek philosophy. From
Thales' first attempt to characterise matter, to Democritus' deduction
that matter ought to reduce to an invariant state, the Ptolemaic
astronomy of a crystalline firmament, and Aristotle's book
PhysicsPhysics (an
early book on physics, which attempted to analyze and define motion
from a philosophical point of view), various Greek philosophers
advanced their own theories of nature.
PhysicsPhysics was known as natural
philosophy until the late 18th century.[28]
By the 19th century, physics was realised as a discipline distinct
from philosophy and the other sciences. Physics, as with the rest of
science, relies on philosophy of science and its "scientific method"
to advance our knowledge of the physical world.[29] The scientific
method employs a priori reasoning as well as a posteriori reasoning
and the use of
Bayesian inferenceBayesian inference to measure the validity of a given
theory.[30]
The development of physics has answered many questions of early
philosophers, but has also raised new questions. Study of the
philosophical issues surrounding physics, the philosophy of physics,
involves issues such as the nature of space and time, determinism, and
metaphysical outlooks such as empiricism, naturalism and realism.[31]
Many physicists have written about the philosophical implications of
their work, for instance Laplace, who championed causal
determinism,[32] and Erwin Schrödinger, who wrote on quantum
mechanics.[33][34] The mathematical physicist
Roger PenroseRoger Penrose has been
called a Platonist by Stephen Hawking,[35] a view Penrose discusses in
his book, The Road to Reality.[36] Hawking refers to himself as an
"unashamed reductionist" and takes issue with Penrose's views.[37]
Core theories
Further information:
Branches of physicsBranches of physics and Outline of physics
Though physics deals with a wide variety of systems, certain theories
are used by all physicists. Each of these theories were experimentally
tested numerous times and found to be an adequate approximation of
nature. For instance, the theory of classical mechanics accurately
describes the motion of objects, provided they are much larger than
atoms and moving at much less than the speed of light. These theories
continue to be areas of active research today. Chaos theory, a
remarkable aspect of classical mechanics was discovered in the 20th
century, three centuries after the original formulation of classical
mechanics by
Isaac NewtonIsaac Newton (1642–1727).
These central theories are important tools for research into more
specialised topics, and any physicist, regardless of their
specialisation, is expected to be literate in them. These include
classical mechanics, quantum mechanics, thermodynamics and statistical
mechanics, electromagnetism, and special relativity.
Classical physics
Main article: Classical physics

Classical physicsClassical physics includes the traditional branches and topics that
were recognised and well-developed before the beginning of the 20th
century—classical mechanics, acoustics, optics, thermodynamics, and
electromagnetism.
Classical mechanicsClassical mechanics is concerned with bodies acted
on by forces and bodies in motion and may be divided into statics
(study of the forces on a body or bodies not subject to an
acceleration), kinematics (study of motion without regard to its
causes), and dynamics (study of motion and the forces that affect it);
mechanics may also be divided into solid mechanics and fluid mechanics
(known together as continuum mechanics), the latter include such
branches as hydrostatics, hydrodynamics, aerodynamics, and pneumatics.
AcousticsAcoustics is the study of how sound is produced, controlled,
transmitted and received.[38] Important modern branches of acoustics
include ultrasonics, the study of sound waves of very high frequency
beyond the range of human hearing; bioacoustics, the physics of animal
calls and hearing,[39] and electroacoustics, the manipulation of
audible sound waves using electronics.[40]
Optics, the study of light, is concerned not only with visible light
but also with infrared and ultraviolet radiation, which exhibit all of
the phenomena of visible light except visibility, e.g., reflection,
refraction, interference, diffraction, dispersion, and polarization of
light.
HeatHeat is a form of energy, the internal energy possessed by the
particles of which a substance is composed; thermodynamics deals with
the relationships between heat and other forms of energy. Electricity
and magnetism have been studied as a single branch of physics since
the intimate connection between them was discovered in the early 19th
century; an electric current gives rise to a magnetic field, and a
changing magnetic field induces an electric current. Electrostatics
deals with electric charges at rest, electrodynamics with moving
charges, and magnetostatics with magnetic poles at rest.
Modern physics
Main article: Modern physics

Classical physicsClassical physics is generally concerned with matter and energy on the
normal scale of observation, while much of modern physics is concerned
with the behavior of matter and energy under extreme conditions or on
a very large or very small scale. For example, atomic and nuclear
physics studies matter on the smallest scale at which chemical
elements can be identified. The physics of elementary particles is on
an even smaller scale since it is concerned with the most basic units
of matter; this branch of physics is also known as high-energy physics
because of the extremely high energies necessary to produce many types
of particles in particle accelerators. On this scale, ordinary,
commonsense notions of space, time, matter, and energy are no longer
valid.[41]
The two chief theories of modern physics present a different picture
of the concepts of space, time, and matter from that presented by
classical physics.
Classical mechanicsClassical mechanics approximates nature as
continuous, while quantum theory is concerned with the discrete nature
of many phenomena at the atomic and subatomic level and with the
complementary aspects of particles and waves in the description of
such phenomena. The theory of relativity is concerned with the
description of phenomena that take place in a frame of reference that
is in motion with respect to an observer; the special theory of
relativity is concerned with relative uniform motion in a straight
line and the general theory of relativity with accelerated motion and
its connection with gravitation. Both quantum theory and the theory of
relativity find applications in all areas of modern physics.[42]
Difference between classical and modern physics

The basic domains of physics

While physics aims to discover universal laws, its theories lie in
explicit domains of applicability. Loosely speaking, the laws of
classical physics accurately describe systems whose important length
scales are greater than the atomic scale and whose motions are much
slower than the speed of light. Outside of this domain, observations
do not match predictions provided by classical mechanics. Albert
Einstein contributed the framework of special relativity, which
replaced notions of absolute time and space with spacetime and allowed
an accurate description of systems whose components have speeds
approaching the speed of light. Max Planck, Erwin Schrödinger, and
others introduced quantum mechanics, a probabilistic notion of
particles and interactions that allowed an accurate description of
atomic and subatomic scales. Later, quantum field theory unified
quantum mechanics and special relativity.
General relativityGeneral relativity allowed
for a dynamical, curved spacetime, with which highly massive systems
and the large-scale structure of the universe can be well-described.
General relativityGeneral relativity has not yet been unified with the other fundamental
descriptions; several candidate theories of quantum gravity are being
developed.

Relation to other fields

This parabola-shaped lava flow illustrates the application of
mathematics in physics—in this case, Galileo's law of falling
bodies.

Prerequisites
MathematicsMathematics provides a compact and exact language used to describe of
the order in nature. This was noted and advocated by Pythagoras,[43]
Plato,[44] Galileo,[45] and Newton.
PhysicsPhysics uses mathematics[46] to organise and formulate experimental
results. From those results, precise or estimated solutions,
quantitative results from which new predictions can be made and
experimentally confirmed or negated. The results from physics
experiments are numerical measurements. Technologies based on
mathematics, like computation have made computational physics an
active area of research.

The distinction between mathematics and physics is clear-cut, but not
always obvious, especially in mathematical physics.

OntologyOntology is a prerequisite for physics, but not for mathematics. It
means physics is ultimately concerned with descriptions of the real
world, while mathematics is concerned with abstract patterns, even
beyond the real world. Thus physics statements are synthetic, while
mathematical statements are analytic.
MathematicsMathematics contains hypotheses,
while physics contains theories.
MathematicsMathematics statements have to be
only logically true, while predictions of physics statements must
match observed and experimental data.
The distinction is clear-cut, but not always obvious. For example,
mathematical physics is the application of mathematics in physics. Its
methods are mathematical, but its subject is physical.[47] The
problems in this field start with a "mathematical model of a physical
situation" (system) and a "mathematical description of a physical law"
that will be applied to that system. Every mathematical statement used
for solving has a hard-to-find physical meaning. The final
mathematical solution has an easier-to-find meaning, because it is
what the solver is looking for.[clarification needed]
PhysicsPhysics is a branch of fundamental science, not practical science.
PhysicsPhysics is also called "the fundamental science" because the subject
of study of all branches of natural science like chemistry, astronomy,
geology, and biology are constrained by laws of physics,[48] similar
to how chemistry is often called the central science because of its
role in linking the physical sciences. For example, chemistry studies
properties, structures, and reactions of matter (chemistry's focus on
the atomic scale distinguishes it from physics). Structures are formed
because particles exert electrical forces on each other, properties
include physical characteristics of given substances, and reactions
are bound by laws of physics, like conservation of energy, mass, and
charge.
PhysicsPhysics is applied in industries like engineering and medicine.

Application and influence
Main article: Applied physics

Archimedes' screw, a simple machine for lifting

The application of physical laws in lifting liquids

Applied physicsApplied physics is a general term for physics research which is
intended for a particular use. An applied physics curriculum usually
contains a few classes in an applied discipline, like geology or
electrical engineering. It usually differs from engineering in that an
applied physicist may not be designing something in particular, but
rather is using physics or conducting physics research with the aim of
developing new technologies or solving a problem.
The approach is similar to that of applied mathematics. Applied
physicists use physics in scientific research. For instance, people
working on accelerator physics might seek to build better particle
detectors for research in theoretical physics.
PhysicsPhysics is used heavily in engineering. For example, statics, a
subfield of mechanics, is used in the building of bridges and other
static structures. The understanding and use of acoustics results in
sound control and better concert halls; similarly, the use of optics
creates better optical devices. An understanding of physics makes for
more realistic flight simulators, video games, and movies, and is
often critical in forensic investigations.
With the standard consensus that the laws of physics are universal and
do not change with time, physics can be used to study things that
would ordinarily be mired in uncertainty. For example, in the study of
the origin of the earth, one can reasonably model earth's mass,
temperature, and rate of rotation, as a function of time allowing one
to extrapolate forward or backward in time and so predict future or
prior events. It also allows for simulations in engineering which
drastically speed up the development of a new technology.
But there is also considerable interdisciplinarity in the physicist's
methods, so many other important fields are influenced by physics
(e.g., the fields of econophysics and sociophysics).
Research
Scientific method
Physicists use the scientific method to test the validity of a
physical theory. By using a methodical approach to compare the
implications of a theory with the conclusions drawn from its related
experiments and observations, physicists are better able to test the
validity of a theory in a logical, unbiased, and repeatable way. To
that end, experiments are performed and observations are made in order
to determine the validity or invalidity of the theory.[49]
A scientific law is a concise verbal or mathematical statement of a
relation which expresses a fundamental principle of some theory, such
as Newton's law of universal gravitation.[50]
TheoryTheory and experiment
Main articles:
Theoretical physicsTheoretical physics and Experimental physics

Theorists seek to develop mathematical models that both agree with
existing experiments and successfully predict future experimental
results, while experimentalists devise and perform experiments to test
theoretical predictions and explore new phenomena. Although theory and
experiment are developed separately, they are strongly dependent upon
each other. Progress in physics frequently comes about when
experimentalists make a discovery that existing theories cannot
explain, or when new theories generate experimentally testable
predictions, which inspire new experiments.[51]
Physicists who work at the interplay of theory and experiment are
called phenomenologists, who study complex phenomena observed in
experiment and work to relate them to a fundamental theory.[52]
Theoretical physicsTheoretical physics has historically taken inspiration from
philosophy; electromagnetism was unified this way.[d] Beyond the known
universe, the field of theoretical physics also deals with
hypothetical issues,[e] such as parallel universes, a multiverse, and
higher dimensions. Theorists invoke these ideas in hopes of solving
particular problems with existing theories. They then explore the
consequences of these ideas and work toward making testable
predictions.
Experimental physicsExperimental physics expands, and is expanded by, engineering and
technology. Experimental physicists involved in basic research design
and perform experiments with equipment such as particle accelerators
and lasers, whereas those involved in applied research often work in
industry developing technologies such as magnetic resonance imaging
(MRI) and transistors. Feynman has noted that experimentalists may
seek areas which are not well-explored by theorists.[53]

Scope and aims

PhysicsPhysics involves modeling the natural world with theory, usually
quantitative. Here, the path of a particle is modeled with the
mathematics of calculus to explain its behavior: the purview of the
branch of physics known as mechanics.

PhysicsPhysics covers a wide range of phenomena, from elementary particles
(such as quarks, neutrinos, and electrons) to the largest
superclusters of galaxies. Included in these phenomena are the most
basic objects composing all other things. Therefore, physics is
sometimes called the "fundamental science".[48]
PhysicsPhysics aims to
describe the various phenomena that occur in nature in terms of
simpler phenomena. Thus, physics aims to both connect the things
observable to humans to root causes, and then connect these causes
together.
For example, the ancient Chinese observed that certain rocks
(lodestone and magnetite) were attracted to one another by an
invisible force. This effect was later called magnetism, which was
first rigorously studied in the 17th century. But even before the
Chinese discovered magnetism, the ancient Greeks knew of other objects
such as amber, that when rubbed with fur would cause a similar
invisible attraction between the two.[54] This was also first studied
rigorously in the 17th century and came to be called electricity.
Thus, physics had come to understand two observations of nature in
terms of some root cause (electricity and magnetism). However, further
work in the 19th century revealed that these two forces were just two
different aspects of one force—electromagnetism. This process of
"unifying" forces continues today, and electromagnetism and the weak
nuclear force are now considered to be two aspects of the electroweak
interaction.
PhysicsPhysics hopes to find an ultimate reason (
TheoryTheory of
Everything) for why nature is as it is (see section Current research
below for more information).[55]
ResearchResearch fields
Contemporary research in physics can be broadly divided into nuclear
and particle physics; condensed matter physics; atomic, molecular, and
optical physics; astrophysics; and applied physics. Some physics
departments also support physics education research and physics
outreach.[56]
Since the 20th century, the individual fields of physics have become
increasingly specialised, and today most physicists work in a single
field for their entire careers. "Universalists" such as Albert
Einstein (1879–1955) and
Lev LandauLev Landau (1908–1968), who worked in
multiple fields of physics, are now very rare.[f]
The major fields of physics, along with their subfields and the
theories and concepts they employ, are shown in the following table.

A simulated event in the CMS detector of the Large Hadron Collider,
featuring a possible appearance of the Higgs boson.

ParticleParticle physics is the study of the elementary constituents of matter
and energy and the interactions between them.[57] In addition,
particle physicists design and develop the high energy
accelerators,[58] detectors,[59] and computer programs[60] necessary
for this research. The field is also called "high-energy physics"
because many elementary particles do not occur naturally but are
created only during high-energy collisions of other particles.[61]
Currently, the interactions of elementary particles and fields are
described by the Standard Model.[62] The model accounts for the 12
known particles of matter (quarks and leptons) that interact via the
strong, weak, and electromagnetic fundamental forces.[62] Dynamics are
described in terms of matter particles exchanging gauge bosons
(gluons, W and Z bosons, and photons, respectively).[63] The Standard
Model also predicts a particle known as the Higgs boson.[62] In July
2012 CERN, the European laboratory for particle physics, announced the
detection of a particle consistent with the Higgs boson,[64] an
integral part of a Higgs mechanism.
Nuclear physicsNuclear physics is the field of physics that studies the constituents
and interactions of atomic nuclei. The most commonly known
applications of nuclear physics are nuclear power generation and
nuclear weapons technology, but the research has provided application
in many fields, including those in nuclear medicine and magnetic
resonance imaging, ion implantation in materials engineering, and
radiocarbon dating in geology and archaeology.
Atomic, molecular, and optical physics
Main article: Atomic, molecular, and optical physics
Atomic, molecular, and optical physicsAtomic, molecular, and optical physics (AMO) is the study of
matter–matter and light–matter interactions on the scale of single
atoms and molecules. The three areas are grouped together because of
their interrelationships, the similarity of methods used, and the
commonality of their relevant energy scales. All three areas include
both classical, semi-classical and quantum treatments; they can treat
their subject from a microscopic view (in contrast to a macroscopic
view).
Atomic physicsAtomic physics studies the electron shells of atoms. Current research
focuses on activities in quantum control, cooling and trapping of
atoms and ions,[65][66][67] low-temperature collision dynamics and the
effects of electron correlation on structure and dynamics. Atomic
physics is influenced by the nucleus (see, e.g., hyperfine splitting),
but intra-nuclear phenomena such as fission and fusion are considered
part of nuclear physics.
Molecular physics focuses on multi-atomic structures and their
internal and external interactions with matter and light. Optical
physics is distinct from optics in that it tends to focus not on the
control of classical light fields by macroscopic objects but on the
fundamental properties of optical fields and their interactions with
matter in the microscopic realm.
Condensed matter physics
Main article: Condensed matter physics

Velocity-distribution data of a gas of rubidium atoms, confirming the
discovery of a new phase of matter, the Bose–Einstein condensate

Condensed matter physicsCondensed matter physics is the field of physics that deals with the
macroscopic physical properties of matter.[68] In particular, it is
concerned with the "condensed" phases that appear whenever the number
of particles in a system is extremely large and the interactions
between them are strong.[69]
The most familiar examples of condensed phases are solids and liquids,
which arise from the bonding by way of the electromagnetic force
between atoms.[70] More exotic condensed phases include the
superfluid[71] and the Bose–Einstein condensate[72] found in certain
atomic systems at very low temperature, the superconducting phase
exhibited by conduction electrons in certain materials,[73] and the
ferromagnetic and antiferromagnetic phases of spins on atomic
lattices.[74]
Condensed matter physicsCondensed matter physics is the largest field of contemporary physics.
Historically, condensed matter physics grew out of solid-state
physics, which is now considered one of its main subfields.[75] The
term condensed matter physics was apparently coined by Philip Anderson
when he renamed his research group—previously solid-state
theory—in 1967.[76] In 1978, the Division of
SolidSolid State
PhysicsPhysics of
the American Physical
SocietySociety was renamed as the Division of Condensed
MatterMatter Physics.[75]
Condensed matter physicsCondensed matter physics has a large overlap with
chemistry, materials science, nanotechnology and engineering.[69]
Astrophysics
Main articles:
AstrophysicsAstrophysics and Physical cosmology

The deepest visible-light image of the universe, the Hubble Ultra Deep
Field

AstrophysicsAstrophysics and astronomy are the application of the theories and
methods of physics to the study of stellar structure, stellar
evolution, the origin of the Solar System, and related problems of
cosmology. Because astrophysics is a broad subject, astrophysicists
typically apply many disciplines of physics, including mechanics,
electromagnetism, statistical mechanics, thermodynamics, quantum
mechanics, relativity, nuclear and particle physics, and atomic and
molecular physics.[77]
The discovery by
Karl JanskyKarl Jansky in 1931 that radio signals were emitted
by celestial bodies initiated the science of radio astronomy. Most
recently, the frontiers of astronomy have been expanded by space
exploration. Perturbations and interference from the earth's
atmosphere make space-based observations necessary for infrared,
ultraviolet, gamma-ray, and X-ray astronomy.
Physical cosmologyPhysical cosmology is the study of the formation and evolution of the
universe on its largest scales. Albert Einstein's theory of relativity
plays a central role in all modern cosmological theories. In the early
20th century, Hubble's discovery that the universe is expanding, as
shown by the Hubble diagram, prompted rival explanations known as the
steady state universe and the Big Bang.
The
Big BangBig Bang was confirmed by the success of
Big BangBig Bang nucleosynthesis
and the discovery of the cosmic microwave background in 1964. The Big
Bang model rests on two theoretical pillars: Albert Einstein's general
relativity and the cosmological principle. Cosmologists have recently
established the ΛCDM model of the evolution of the universe, which
includes cosmic inflation, dark energy, and dark matter.
Numerous possibilities and discoveries are anticipated to emerge from
new data from the Fermi Gamma-ray
SpaceSpaceTelescopeTelescope over the upcoming
decade and vastly revise or clarify existing models of the
universe.[78][79] In particular, the potential for a tremendous
discovery surrounding dark matter is possible over the next several
years.[80] Fermi will search for evidence that dark matter is composed
of weakly interacting massive particles, complementing similar
experiments with the
Large Hadron ColliderLarge Hadron Collider and other underground
detectors.
IBEXIBEX is already yielding new astrophysical discoveries: "No one knows
what is creating the ENA (energetic neutral atoms) ribbon" along the
termination shock of the solar wind, "but everyone agrees that it
means the textbook picture of the heliosphere—in which the Solar
System's enveloping pocket filled with the solar wind's charged
particles is plowing through the onrushing 'galactic wind' of the
interstellar medium in the shape of a comet—is wrong."[81]
Current research
Further information: List of unsolved problems in physics

A typical event described by physics: a magnet levitating above a
superconductor demonstrates the Meissner effect.

ResearchResearch in physics is continually progressing on a large number of
fronts.
In condensed matter physics, an important unsolved theoretical problem
is that of high-temperature superconductivity.[82] Many condensed
matter experiments are aiming to fabricate workable spintronics and
quantum computers.[69][83]
In particle physics, the first pieces of experimental evidence for
physics beyond the
Standard ModelStandard Model have begun to appear. Foremost among
these are indications that neutrinos have non-zero mass. These
experimental results appear to have solved the long-standing solar
neutrino problem, and the physics of massive neutrinos remains an area
of active theoretical and experimental research. The Large Hadron
Collider has already found the Higgs Boson, but future research aims
to prove or disprove the supersymmetry, which extends the Standard
Model of particle physics.
ResearchResearch on the nature of the major
mysteries of dark matter and dark energy is also currently
ongoing.[84]
Theoretical attempts to unify quantum mechanics and general relativity
into a single theory of quantum gravity, a program ongoing for over
half a century, have not yet been decisively resolved. The current
leading candidates are M-theory, superstring theory and loop quantum
gravity.
Many astronomical and cosmological phenomena have yet to be
satisfactorily explained, including the origin of ultra-high energy
cosmic rays, the baryon asymmetry, the acceleration of the universe
and the anomalous rotation rates of galaxies.
Although much progress has been made in high-energy, quantum, and
astronomical physics, many everyday phenomena involving
complexity,[85] chaos,[86] or turbulence[87] are still poorly
understood. Complex problems that seem like they could be solved by a
clever application of dynamics and mechanics remain unsolved; examples
include the formation of sandpiles, nodes in trickling water, the
shape of water droplets, mechanisms of surface tension catastrophes,
and self-sorting in shaken heterogeneous collections.[88]
These complex phenomena have received growing attention since the
1970s for several reasons, including the availability of modern
mathematical methods and computers, which enabled complex systems to
be modeled in new ways. Complex physics has become part of
increasingly interdisciplinary research, as exemplified by the study
of turbulence in aerodynamics and the observation of pattern formation
in biological systems. In the 1932 Annual Review of Fluid Mechanics,
Horace LambHorace Lamb said:[89]

I am an old man now, and when I die and go to heaven there are two
matters on which I hope for enlightenment. One is quantum
electrodynamics, and the other is the turbulent motion of fluids. And
about the former I am rather optimistic.

^ The term 'universe' is defined as everything that physically exists:
the entirety of space and time, all forms of matter, energy and
momentum, and the physical laws and constants that govern them.
However, the term 'universe' may also be used in slightly different
contextual senses, denoting concepts such as the cosmos or the
philosophical world.
^ Francis Bacon's 1620
Novum OrganumNovum Organum was critical in the development
of scientific method.[10]
^
CalculusCalculus was independently developed at around the same time by
Gottfried Wilhelm Leibniz; while Leibniz was the first to publish his
work and develop much of the notation used for calculus today, Newton
was the first to develop calculus and apply it to physical problems.
See also Leibniz–Newton calculus controversy
^ See, for example, the influence of Kant and Ritter on Ørsted.
^ Concepts which are denoted hypothetical can change with time. For
example, the atom of nineteenth-century physics was denigrated by
some, including Ernst Mach's critique of Ludwig Boltzmann's
formulation of statistical mechanics. By the end of World War II, the
atom was no longer deemed hypothetical.
^ Yet, universalism is encouraged in the culture of physics. For
example, the World Wide Web, which was innovated at
CERNCERN by Tim
Berners-Lee, was created in service to the computer infrastructure of
CERN, and was/is intended for use by physicists worldwide. The same
might be said for arXiv.org

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Encyclopedia of
PhysicsPhysics at Scholarpedia
de Haas, Paul, Historic Papers in
PhysicsPhysics (20th Century) at the
Wayback MachineWayback Machine (archived 26 August 2009)
PhysicsCentral – Web portal run by the American Physical Society
Physics.org – Web portal run by the Institute of Physics
The Skeptic's Guide to Physics
Usenet
PhysicsPhysics FAQ – A FAQ compiled by sci.physics and other physics
newsgroups
Website of the Nobel Prize in physics
World of
PhysicsPhysics An online encyclopedic dictionary of physics
Nature: Physics
PhysicsPhysics announced 17 July 2008 by the American Physical Society
Physics/Publications at Curlie (based on DMOZ)
Physicsworld.com – News website from
Institute of PhysicsInstitute of Physics Publishing
PhysicsPhysics Central – includes articles on astronomy, particle physics,
and mathematics.
The Vega Science Trust – science videos, including physics
Video:
PhysicsPhysics "Lightning" Tour with Justin Morgan
52-part video course: The Mechanical Universe...and Beyond Note: also
available at 01 – Introduction at Google Videos
HyperPhysics website – HyperPhysics, a physics and astronomy
mind-map from Georgia State University

Organizations

AIP.org – Website of the American Institute of Physics
APS.org – Website of the American Physical Society
IOP.org – Website of the Institute of Physics
PlanetPhysics.org
Royal
SocietySociety – Although not exclusively a physics institution, it
has a strong history of physics
SPS National – Website of the
SocietySociety of
PhysicsPhysics Students